Torricelli, Evangelista (1608-1647)
Italian physicist
As a scientist, Evangelista Torricelli became well known for his study of the motion of fluids, and was declared the father of hydrodynamics by Ernst Mach. Torricelli also conducted experiments on gases, though the term was not then in use. Most notably, Torricelli settled an argument about the nature of gases and the existence of the vacuum. Aristotle believed that a vacuum could not exist. Though Galileo disagreed, he contended that the action of suction (in a water pump, for example) was produced by a vacuum itself and not by the pressure of the air pushing on the liquid being pumped. Despite his argument, Torricelli noticed that water could be pumped only a finite distance through a vertical tube before it ceased to move any further and set out to examine this paradox, inventing the first barometer in the process.
During his experimentation, Torricelli filled a one-ended glass tube with mercury, then immersed the open end in a dish of more mercury, placing the tube in a upright position. He found that about 30 in (76 cm) of mercury remained in the tube, deducing that a vacuum had been created above the mercury in the tube, and that the mercury was held in place not by the vacuum, but by the pressure of air pushing down the mercury in the dish. Thus, he demonstrated the existence of a vacuum, showed why pumps then in use could only move liquids vertically a certain distance (the distance determined by the pressure of the surrounding air), and created an instrument capable of measuring air pressure.
Torricelli's invention of the barometer led to a burst of both theoretical and experimental work in physics and meteorology. Torricelli also made a contribution to meteorology with his suggestion that wind was not caused by the "exhalations" of vapors from a damp Earth, but by differences in the density of air that, in turn, were caused by differences in the air temperature.
Born near Ravenna, Italy, Torricelli was first educated in local Jesuit schools and showed such brilliance that he was sent to Rome to study with Galileo's former student Benedetto Castelli (1578–1643). Through Castelli he first corresponded with and met Galileo, finally becoming his secretary and assistant. A few months after Galileo's death in 1642, Torricelli accepted Galileo's old position as court mathematician and philosopher to the Grand Duke of Tuscany, a position he held until his own death, before his fortieth birthday.
Torricelli's investigations in mathematics played an important role in scientific history as well. Based on Francesco Cavalieri's "geometry of indivisibles," Torricelli worked out equations upon curves, solids, and their rotations, helping to bridge the gap between Greek geometry and calculus. Along with the work of René Descartes, Pierre de Fermat, Gilles Personne de Roberval, and others, these works enabled Isaac Newton and Gottfried Wilhelm Leibniz to give calculus its first complete formulation.
Atmospheric Pressure
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